SIM CARDS
SIM cards have
evolved a lot over the years. While they have maintained a relative thickness
of just under 1mm, their surface area has steadily decreased, from the credit
card-sized plates used in the earliest cell phones to the nanoSIMs of today's
devices. Many carriers offer branded SIM cards with cutouts for all three
modern sizes, so users can choose which version they want to insert depending
on their device. There are also adapters so nanoSIM cards can fit into slots
meant for microSIM or Regular SIM cards. A SIM card is a smart card that is used in mobile phones,
to identify the client. SIM stands for Subscriber Identity Module. A SIM card
has a microchip,
and its use is protected by a PIN. When the phone is powered on,
a special number called IMSI (International
Mobile Subscriber Identity) is broadcast. The microchip is also needed
for some encryption and decryption.
The SIM card, and the device it is use in (the mobile phone) are often referred
to as Mobile station.
Types of SIM Card:
There are two types of SIM cards that is GSM and CDMA:
GSM:
GSM technology stands for Global System for Mobiles and its
foundation can be credited to Bell Laboratories in 1970. It basically
uses circuit switched system and divides each 200 kHz signal into 8 25
kHz time slots and operates in 900 MHz, 800 MHz and 1.8GHz bands. It uses a
narrow band transmission technique- basically Time Division Access Multiplexing.
The data transfer rates vary from 64kbps to 120kbps.
CDMA:
CDMA means code division multiple access which explains about
communication channel principle that employs spread-spectrum technology and a
special coding scheme which are time division multiplexing scheme and frequency
division multiplexing scheme.
How does a SIM card work?
SIM
Card has a small amount of memory and a very low-powered processor, the SIM
card not only enables communication between the phone and its carrier, but
stores information such as phone numbers, security data and more.
SIM cards
are transferrable. If your Phone runs out of power and you desperately need to
make a call or connect to the internet, you can just swap the SIM into another Phone
and use it
Conclusion
In the end, SIM cards are both a blessing and a curse. They
grant freedom to customers to move from phone to phone as long as those phones
are compliant with GSM standards, but can prove annoying if the card itself is
somehow lost or damaged since they hold so much crucial data.
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